Systems and methods for controlling fluid feed to an aerosol generator

ABSTRACT

A method for controlling the supply of liquid to an aerosol generator comprises operating a liquid supply system to supply a liquid to a vibratable aperture plate of an aerosol generator which senses an amount of liquid adhering to the vibratable aperture plate, and controls operation of the liquid supply system to adjust the amount of liquid adhering to the vibratable aperture plate.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part application of U.S.patent application Ser. No. 09/318,552, filed May 27, 1999, which is acontinuation application of U.S. patent application Ser. No. 08/417,311,filed Apr. 5, 1995 (now U.S. Pat. No. 5,938,117), which is acontinuation-in-part application of U.S. patent application Ser. No.08/163,850 filed on Dec. 7, 1993, which is a continuation-in-part ofU.S. patent application Ser. No. 07/726,777 filed on Jul. 8, 1991 (nowabandoned), which is a continuation-in-part of U.S. patent applicationSer. No. 07/691,584 filed on Apr. 24, 1991, now U.S. Pat. No. 5,164,740.The complete disclosures of all these references are herein incorporatedby reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to improved aerosolizing devices,particularly but not exclusively for atomizing liquid medicaments to beinhaled, and to a method of constructing such devices.

[0003] A wide variety of procedures have been proposed to deliver a drugto a patient. Of particular interest to the present invention are drugdelivery procedures where the drug is a liquid and is dispensed in theform of fine liquid droplets for inhalation by a patient. A variety ofdevices have been proposed for forming the dispersion, including air jetnebulizers, ultrasonic nebulizers and metered dose inhalers (MDIs). Airjet nebulizers usually utilize a high pressure air compressor and abaffle system that separates the large particles from the spray.Ultrasonic nebulizers generate ultrasonic waves with an oscillatingpiezoelectric crystal to produce liquid droplets. Another type ofultrasonic nebulizer is described in U.S. Pat. Nos. 5,261,601 and4,533,082. Typical MDIs usually employ a gas propellant, such as a CFC,which carries the therapeutic substance and is sprayed into the mouth ofthe patient.

[0004] The present applicant has also proposed a variety ofaerosolization devices for atomizing liquid solutions. For example, oneexemplary atomization apparatus is described in U.S. Pat. No. 5,164,740,the complete disclosure of which is herein incorporated by reference.The atomization apparatus comprises an ultrasonic transducer and anaperture plate attached to the transducer. The aperture plate includestapered apertures which are employed to produce small liquid droplets.The transducer vibrates the plate at relatively high frequencies so thatwhen the liquid is placed in contact with the rear surface of theaperture plate and the plate is vibrated, liquid droplets will beejected through the apertures. The apparatus described in US 5,164,740has been instrumental in producing small liquid droplets without theneed for placing a fluidic chamber in contact with the aperture plate.Instead, small volumes of liquid are delivered to the rear surface ofthe aperture plate and held in place by surface tension forces.

[0005] Modified atomization apparatus are described in U.S. Pat. Nos.5,586,550 and 5,758,637, the complete disclosures of which are hereinincorporated by reference. The two references describe a liquid dropletgenerator which is particularly useful in producing a high flow ofdroplets in, a narrow size distribution. As described in U.S. Pat. No.5,586,550, the use of a dome shaped aperture plate is advantageous inallowing more of the apertures to eject liquid droplets.

[0006] One requirement of such aerosolization devices is the need tosupply liquid to the aperture plate. In some applications, such as whendelivering aerosolized medicaments to the lungs, it may be desirable toregulate the supply of the liquid to the aperture plate so that properpulmonary delivery of the drug may occur. For example, if too muchliquid is supplied, the aerosol generator may be unable to aerosolizefully all of the delivered liquid. On the other hand, if too littleliquid is supplied, the user may not receive a sufficient dosage.Further, a metering process may be needed to ensure that a unit dosageamount of the liquid is delivered to the aerosol generator. This may bechallenging if the user requires several inhalations in order to inhalethe unit dose amount.

[0007] The present invention is related to liquid feed systems andmethods for delivering liquids to the aerosol generator to facilitateaerosolization of the liquid.

SUMMARY OF THE INVENTION

[0008] The invention provides exemplary aerosolization devices andmethods for aerosolizing liquids. In one embodiment, an aerosolizationdevice comprises a liquid supply system that is adapted to hold a supplyof liquid, and an aerosol generator that is configured to aerosolizeliquid supplied from the liquid supply system. In one aspect, theaerosol generator may comprise a plate having a plurality of aperturesand a vibratable element disposed to vibrate the plate. Theaerosolization device further comprises a sensor configured to sense anamount of unaerosolized liquid supplied to the aerosol generator, and acontroller to control operation of the liquid supply system based oninformation received from the sensor. In this way, during aerosolizationthe amount of unaerosolized liquid supplied to the aerosol generatorremains within a certain range. In this manner, the device is configuredto prevent either too much or too little liquid from being supplied tothe aerosol generator at any one time.

[0009] In one aspect, the sensor comprises a strain gauge coupled to theaerosol generator for detecting variations in strain caused by varyingamounts of unaerosolized liquid adhering to the aerosol generator. Thestrain gauge may comprise a piezoelectric element coupled to the aerosolgenerator such that variations in an electrical characteristic (e.g.impedance) are representative of unaerosolized liquid adhering to theaerosol generator. The piezoelectric element may also act as atransducer disposed to vibrate an aperture plate in the aerosolgenerator.

[0010] In another aspect, the sensor may comprise an optical sensor. Theoptical sensor may be configured to sense the presence or absence ofunaerosolized liquid at a certain location on the aerosol generator. Thecertain location may be spaced from where liquid is supplied to theaerosol generator.

[0011] In yet another aspect, the sensor may be a conductivity sensorthat is configured to sense electrical conductivity between at least twopoints across a surface of the aerosol generator on which unaerosolizedliquid may adhere. At least one of the points may be spaced from whereliquid is supplied to the aerosol generator. Further, at least one ofthe points may be closer to where liquid is supplied to the aerosolgenerator than another one of the points. In this way, sensingelectrical conductivity may give an indication of unaerosolized liquiddistribution across the aerosol generator.

[0012] In one particular embodiment, the amount of unaerosolized liquidon the aerosol generator remains within the range from about 0 to about20 microliters, and more preferably from about 2 microliters to about 20microliters.

[0013] The device may further comprise a housing having a mouthpiece,with the aerosol generator disposed in the housing for delivery ofaerosolized liquid through the mouthpiece. In this way, a drug may beaerosolized and ready for pulmonary delivery upon patient inhalation.

[0014] In another particular aspect, the liquid supply system maycomprise a dispenser for dispensing a certain amount of liquid uponreceipt of an appropriate signal from the controller. In this way, apredetermined amount of liquid may be chosen to ensure the aerosolgenerator is not overloaded at any one time. The device may furthercomprise a meter for limiting the number of times the dispenser isactivated during operation of the aerosol generator. In this way, thetotal liquid delivered by the aerosol generator in any one period ofoperation may be accurately controlled, thereby limiting the risk ofdelivering below or above a recommended dose.

[0015] In yet another particular embodiment, the device may furthercomprise a heater for heating unaerosolized liquid supplied to theaerosol generator. The heater may be adapted to heat the aerosolgenerator to vaporize or burn off residual unaerosolized liquid afteraerosol generator cessation. In this way, residual unaerosolized liquidmay be removed to prevent interference with a subsequent aerosolizationevent. The heater may comprise an electrical resistance heater and anelectrical power supply (e.g. battery) for energizing resistanceheating.

[0016] In another embodiment of the invention, a method for aerosolizinga liquid utilizes an aerosol generator that is operable to aerosolize aliquid. According to the method, a liquid is supplied to the aerosolgenerator from a liquid supply system at an initial flow rate. Duringaerosolization, the amount of supplied liquid remaining unaerosolized issensed and the rate of liquid supply regulated based upon the sensedamount. The rate of liquid supply may be decreased if the sensed amountexceeds a certain value, and the rate of liquid supply may be increasedif the sensed amount falls below a critical level. In this way, it ispossible to prevent or to reduce the extent of supplying too much or toolittle liquid being supplied to the aerosol generator at any one time.

[0017] In one aspect, the method further comprises providing a heaterfor heating unaerosolized liquid supplied to the aerosol generator. Bysensing whether any of the supplied liquid remains unaerosolized aftercessation of the liquid supply, the heater may be operated to vaporizeor burn-off such supplied liquid remaining on the aerosol generator.

[0018] In yet another embodiment of the invention, an aerosolizationdevice comprises a liquid supply system that is adapted to hold a supplyof liquid, and an aerosol generator comprising a plate having aplurality of apertures and an electric transducer disposed to vibratethe plate when energized. A sensor is configured to sense an electricalcharacteristic of the electrical transducer that is dependent upon anamount of unaerosolized liquid adhering to the plate. A controller isprovided to regulate operation of the liquid supply in order to maintainthe amount of unaerosolized liquid adhering to the plate within acertain range during aerosolization.

[0019] In a still further embodiment, a method is provided forcontrolling the supply of a liquid to an aerosol generator. According tothe method, a liquid supply system is operated to supply a liquid to avibratable aperture plate of an aerosol generator. An amount of liquidadhering to the vibratable plate is sensed and is used to control theamount of liquid supplied to the plate. By controlling operation of theliquid supply system, the amount of liquid adhering to the vibratableaperture plate may be regulated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a cross-sectional schematic diagram of an aerosolizationdevice according to the invention.

[0021]FIG. 2 is a schematic diagram showing an alternativeaerosolization device and liquid supply system embodying the presentinvention.

[0022]FIG. 3 is a schematic diagram of one embodiment of a fluid sensoraccording to the invention.

[0023]FIG. 4 is a schematic diagram of one embodiment of a liquid supplysystem according to the invention.

[0024]FIG. 5 is a schematic diagram showing a heater for an aerosolgenerator according to the invention.

[0025]FIG. 6 is a flow chart illustrating one method of controlling thesupply of liquid to an aerosol generator.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0026] The invention provides exemplary aerosolization devices andmethods for controlling the supply of a liquid to an aerosol generator.The invention is applicable to essentially any aerosolizer where liquiddelivered to the aerosolizer may accumulate leading to variation indevice performance. Merely by way of example, the invention may be usedwith atomizers such as those described in U.S. Pat. Nos. 5,140,740,5,938,117, 5,586,550, and 6,014,970, incorporated herein by reference.However, it will be appreciated that the invention is not intended to belimited only to these specific atomizers.

[0027] Aerosolization devices embodying the present inventionconveniently sense the amount of unaerosolized liquid which hasaccumulated at the aerosol generator. This information is used to modifythe rate of supply of liquid to the aerosol generator to maintain theamount of liquid adhering to the aerosol generator within certainlimits. In this way, the aerosol generator is neither oversupplied norunder supplied with liquid, and is able to operate efficiently andeffectively.

[0028] The sensor may take a variety of forms. For example, the sensormay be a piezoelectric device for sensing strains induced on the aerosolgenerator by liquid loads. Alternatively, the sensor may be an opticalsensor, a conductivity sensor, or the like for sensing amounts ofunaerosolized liquid on the aerosol generator. Another feature is thepotential ability to vaporize or burn off unwanted unaerosolized liquidfrom the aerosol generator. The requisite heat may be applied by anelectrical resistance heater, or the like.

[0029] In one embodiment, the supply of liquid to the aerosol generatoris delivered in predetermined quantities. Each predetermined quantitymay be a fraction of a total dose, and thus each delivery of thepredetermined delivery may be counted. When the number of deliveriesmatches the quantity of the total dose, the liquid supply isinterrupted.

[0030] Referring now to FIG. 1, one embodiment of an aerosolizationdevice 10 will be described. Device 10 comprises a housing 12 to holdthe various components of aerosolization device 10. Housing 12 furtherincludes a mouthpiece 14 and one or more vents (not shown) to permit airto enter into housing 12 when a user inhales from mouthpiece 14.Disposed within housing 12 is an aerosol generator 16 that comprises acup-shaped member 18 to which is coupled an aperture plate 20. Anannular piezoelectric element 22 is in contact with aperture plate 20 tocause aperture plate 20 to vibrate when electrical current is suppliedto piezoelectric element 22. Aperture plate 20 is dome-shaped ingeometry and includes a plurality of tapered apertures that narrow fromthe rear surface to the front surface. Exemplary aperture plates andaerosol generators that may be used in aerosolization device 10 aredescribed in U.S. Pat. Nos. 5,086,785, 5,157,372 and 5,309,135,incorporated herein by reference.

[0031] Aerosolization device 10 further includes a liquid feed system 24having a supply of liquid that is to be aerosolized by aerosol generator16. Liquid feed system 24 may be configured to place metered amounts ofliquid onto aperture plate 20. Although not shown, a button or the likemay be employed to dispense the liquid when requested by the user.Conveniently, feed system 24 may be configured to supply a unit dose ofliquid over time to aperture plate 20. As described hereinafter, avariety of sensors may be used to monitor and control the amount ofliquid supplied to aperture plate 20 so that the amount of unaerosolizedliquid remains within a certain range.

[0032] Housing 12 includes an electronics region 26 for holding thevarious electrical components of aerosolization device 10. For example,region 26 may include a printed circuit board 28 which serves as acontroller to control operation of the aerosol generator 16. Morespecifically, circuit board 28 may send (via circuitry not shown) anelectrical signal to piezoelectric element 22 to cause aperture plate 20to be vibrated. A power supply P, such as one or more batteries, iselectrically coupled to circuit board 28 to provide aerosolizationdevice 10 with power. Optionally, a flow sensor may be used to sensepatient inhalation and to operate aerosol generator 16 only when athreshold flow rate has been produced by the user. One example of such aflow sensor is described in copending U.S. patent application Ser. No.09/149,246, filed Sep. 8, 1998, the complete disclosure of which isherein incorporated by reference.

[0033]FIG. 2 illustrates schematically an alternative aerosol generator30 with one fluid supply system according to an embodiment of theinvention. The fluid supply system is configured to maintain a propersupply of liquid to aerosol generator 30. Although described inconnection with aerosol generator 30, it will be appreciated that thesystem of FIG. 2 may be used with any of the aerosolization devicesdescribed herein.

[0034] The aerosol generator 30 is in the form of a cantilevered beam 32on which a piezoelectric oscillator 38 is mounted. The free end 37 ofthe beam 32 is provided with a planar surface through which there aremicroscopic tapered apertures. Fluid 42 in contact with the free end 37is ejected through the tapered apertures producing droplets 44 when thebeam is oscillated at high frequency by the piezoelectric oscillator 38.The fluid supply system 50 continuously transports fluid 51 to wet theoscillating surface 37 via a supply tube 53 ending at a supply nozzle54. The fluid 51 is transported to the surface 37 at a rate which islower than the maximum ejection rate of the apertures 40 to preventoverflow of fluid 42 from the supply side of the oscillating surface 37.A pinch valve 56 controls delivery of the fluid 51 to the oscillatingsurface 37. The fluid supply system 50 is connected to an electronicflow control valve 52 which is connected to an electronic circuit thatdetects the amount of liquid 42 on the oscillating surface 37. In theevent of excessive delivery of fluid, the oscillation amplitudedecreases and the current draw by the piezoelectric element 38decreases. This is because as the load changes, there is a correspondingchange in the impedance of the piezoelectric element. A current sensorcircuit 39 senses the current draw and transmits an overflow signal 41to the flow control valve 52 to reduce the delivery rate of the liquid51 to the surface 37 until the amount of fluid returns to normal level.

[0035] The arrangement described in FIG. 2 utilizes an electricalcharacteristic (e.g. impedance) of the piezoelectric element 38 which isdependent upon the liquid load on aerosol generator 30. By sensing theelectrical characteristic, either in absolute or relative terms, it ispossible to control the rate of liquid supply to the aerosol generatorin order to maintain the amount of unaerosolized liquid adhering to thebeam 32 within certain limits. In other words, if the amount ofunaerosolized liquid on the beam 32 falls below a lower limit, the flowrate may be increased to prevent the aerosol generator from running dry.On the other hand, if the amount of unaerosolized liquid on the beam 32rises above an upper limit, the flow rate may be decreased or eventemporarily suspended to prevent overloading of the aerosol generator.As previously mentioned, such a system may also be used with aerosolgenerator 16 of FIG. 1 by sensing the amount drawn by piezoelectricelement 22.

[0036]FIG. 3 schematically illustrates a conductive sensor 70 that maybe used to sense the volume of fluid on an aperture plate, including anyof those described herein. For convenience of discussion, sensor 70 isdescribed with reference to aerosol generator 18 of FIG. 1. Conductivesensor 70 is used to measure electrical conductivity between two points72,74 above a surface of aperture plate 20 to which unaerosolized liquidadheres. One of the points 72 is located adjacent where liquid isdelivered to the aerosol generator, while the other point 74 is spacedlaterally of where such liquid is delivered. In use, a build-up ofunaerosolized liquid on aperture plate 20 will have no appreciableeffect on electrical conductivity measured by a detector 76, until theunaerosolized liquid bridges the spacing between point 72,74. When thedetector 76 registers a sudden change in conductivity—indicative ofcurrent flowing through unaerosolized liquid—the flow rate of liquidsupply may be reduced to avoid further build-up of liquid. A secondconductive sensor (not shown) may be positioned to detect when theamount of unaerosolized liquid falls below a lower level, for triggeringan increase in liquid flow when required. In this way, conductivity maybe used to maintain the amount of unaerosolized liquid supplied to theaerosol generator within certain limits.

[0037] In another embodiment, the conductive sensor 70 may be replacedwith an optical sensor which, for example, senses the present or absenceof unaerosolized liquid in a certain location, or series of discretelocations on the aperture plate. If the presence of unaerosolized liquidis sensed at an outer location spaced from the point of liquid deliveryto the aerosol generator, the flow rate of liquid supply may be reduced.If the absence of unaerosolized liquid is sensed in another locationspaced inwardly from the outer location, the flow rate of liquid supplymay be increased.

[0038]FIG. 4 schematically illustrates in more detail liquid feed system24 of FIG. 1. Liquid feed system 24 includes a canister 100 configuredto deliver liquid to aperture plate 20 of aerosol generator 16. A sensor102 (be it piezo, conductive or optical) senses the unaerosolized liquidadhering to the aperture plate 20, and relays this information tocontroller 104. Controller 104 controls a dispensing system 106 which,upon receipt of dispensed signal from controller 104, dispenses apredetermined amount of liquid (e.g. 5 microliters) from canister 100.Dispensing system 106 comprises a motor 108 which drives a lead screw110 coupled to a piston 112 associated with canister 100. When thecontroller 104 senses via sensor 102 that the amount of unaerosolizedliquid on the aperture plate 20 has fallen below a lower limit, itactivates motor 108 for a predetermined time, e.g. one second. In thistime, motor 108 turns lead screw 110 causing piston 112 to advance apredetermined amount and hence deliver a measured quantity of liquid tothe aerosol generator.

[0039] A meter 114 is coupled to the motor 108 and to the piezoelectrictransducer 22. The meter 114 counts the number of times the motor 108 isactivated in any period of continuous operation of the aerosolgenerator, i.e., while piezoelectric transducer 22 is vibrating. Themeter 114 serves to prevent the motor 108 from being operated more thana predetermined number of times (e.g., 20) in any one period of use. Inthis way, the user may continue to use the aerosol generator 16 until anappropriate dose has been aerosolized (e.g., 20×5 microliters=100microliters). At this time, operation of the motor 108 is temporarilystopped by the meter 114 and a corresponding signal sent to controller104. Such a signal may enable an indication to be given to the user thata full dose has been delivered.

[0040] In some cases, the user may stop operation without aerosolizingthe full dose. The controller may be configured to record the partialdosage and notify the user when attempting to continue operation.

[0041]FIG. 5 schematically illustrates a heater 120 for an aerosolgenerator, such as aerosol generator 16 of FIG. 1. Heater 120 is usefulwhen unaerosolized liquid remains on the aperture plate 20 after thesupply of liquid has ceased, e.g., because required dose has beendelivered or the user stops operation. Heater 120 is incorporated intothe aerosol generator 16 in order to vaporize or burn off excessunaerosolized liquid on the aperture plate 20. Heater 120 is an annularelectrical resistance heater, and is energized by power source P undercontrol of controller 104. In use, sensor 102 relays information to thecontroller 104 that unaerosolized liquid remains on the aperture plate20 after the supply of liquid through supply system 100 has ceased. Ifthis situation remains unchanged for a predetermined time interval, thecontroller 104 may activate switch 122 to heat aperture plate 20 byheater 120. In this way, excess unaerosolized liquid may be removed,ensuring the aperture plate 20 is clear and ready for reuse.

[0042] Referring now to FIG. 6, one method of controlling the supply ofliquid to an aerosolizing device will now be described. The processbegins at step 200 where an aerosol generator is provided. Liquid issupplied at step 202 to the aerosol generator for aerosolization. Someof the liquid supplied is unaerosolized and accumulates on the aerosolgenerator, and the amount of such liquid is sensed as shown at step 204.The amount of liquid sensed is then compared at step 206 with apredetermined range of amounts, the upper limit of which corresponds tothe maximum desired amount on the aerosol generator, and the lower limitof which corresponds to the minimum desired amount on the aerosolgenerator. If the sensed amount exceeds the upper limit, the flow rateis decreased at step 208, and if the sensed amount falls below the lowerlimit, the flow rate is increased as shown at step 210. The total amountof liquid supplied to the aerosol generator is monitored at step 212. Ifthe total amount is less than a predetermined total dose, the supplycycle is repeated, and if the total amount is equal to the predetermineddose, the supply is terminated at step 218. Any unaerosolized liquid onthe aerosol generator after terminating the supply is burnt off at 220by energizing an electric heater.

[0043] The invention has now been described in detail for purposes ofclarity of understanding. However, it will be appreciated that certainchanges and modifications may be practiced within the scope of theappended claims.

What is claimed is:
 1. An aerosolization device comprising: a liquidsupply system that is adapted to hold a supply of liquid; an aerosolgenerator configured to aerosolize liquid supplied from the liquidsupply system; a sensor that is configured to sense an amount ofunaerosolized liquid supplied to the aerosol generator; and a controllerto control operation of the liquid supply system based on informationreceived from the sensor.
 2. An aerosolization device according to claim1, wherein the aerosol generator comprises a vibratable element and anaperture plate.
 3. An aerosolization device according to claim 2,wherein the aperture plate includes a plurality of tapered apertures. 4.An aerosolization device according to claim 1, wherein the controller isconfigured to maintain the amount of supplied and unaerosolized liquidwithin a certain range during aerosolization.
 5. An aerosolizationdevice according to claim 1, wherein the sensor comprises a strain gaugecoupled to the aerosol generator for detecting variations in strainaccording to variations in the amount of unaerosolized liquid in contactwith the aerosol generator.
 6. An aerosolization device according toclaim 5, wherein the strain gauge comprises a piezoelectric element,with variations in the amount of unaerosolized liquid adhered to theaerosol generator causing corresponding variations in an electricalcharacteristic of the piezoelectric element.
 7. An aerosolization deviceaccording to claim 6, further comprising electrical circuitry configuredto measure variations in impedance of the piezoelectric element.
 8. Anaerosolization device according to claim 6, wherein the piezoelectricelement is disposed to vibrate an aperture plate in the aerosolgenerator.
 9. An aerosolization device according to claim 1, wherein thesensor comprises an optical sensor.
 10. An aerosolization deviceaccording to claim 9, wherein the optical sensor is configured to sensethe presence or absence of supplied and unaerosolized liquid in acertain location on the aerosol generator.
 11. An aerosolization deviceaccording to claim 10, wherein the certain location is spaced from whereliquid is supplied to the aerosol generator.
 12. An aerosolizationdevice according to claim 1, wherein the sensor comprises a conductivesensor configured to sense electrical conductivity between at least twopoints across a surface of the aerosol generator on which supplied andunaerosolized liquid adheres, at least one point being spaced from whereliquid is supplied to the aerosol generator.
 13. An aerosolizationdevice according to claim 12, wherein one of the at least two points iscloser to where liquid is supplied to the aerosol generator than anotherof the at least two points.
 14. An aerosolization device according toclaim 1, wherein the amount of unaerosolized liquid supplied to theaerosol generator remains within the range from about 2 to about 20 μl(microliters).
 15. An aerosolization device according to claim 1,further comprising a housing having a mouthpiece, the aerosol generatorbeing disposed in the housing for delivery of aerosolized liquid throughthe mouthpiece.
 16. An aerosolization device according to claim 1,wherein the liquid supply system comprises a dispenser for dispensing acertain amount of liquid upon receipt of a dispense signal from thecontroller.
 17. An aerosolization device according to claim 16, furthercomprising a meter for limiting the number of times the dispenser isactivated during operation of the aerosol generator.
 18. Anaerosolization device according to claim 1, further comprising a heaterfor heating unaerosolized liquid supplied to the aerosol generator. 19.An aerosolization device according to claim 18, wherein the heater isconfigured to heat the aerosol generator to vaporize the unaerosolizedliquid.
 20. An aerosolization device according to claim 19, wherein theheater comprises an electrical resistance heating element and anelectrical power supply for energizing resistance heating.
 21. Anaerosolization device comprising: a liquid supply system that is adaptedto hold a supply of liquid; an aerosol generator comprising an elementhaving a plurality of apertures and an electrical transducer disposed tovibrate the element when energized; a sensor configured to sense anelectrical characteristic of the electrical transducer that is dependentupon an amount of unaerosolized liquid adhering to the element; and acontroller to control operation of the liquid supply system based on theelectrical characteristic sensed by the sensor, whereby the amount ofunaerosolized liquid adhering to the element is maintained within acertain range during aerosolization.
 22. An aerosolization deviceaccording to claim 21, wherein the electrical transducer comprises apiezoelectric element.
 23. An aerosolization device according to claim22, wherein the electrical characteristic sensed by the sensor is theimpedance of the piezoelectric element.
 24. An aerosolization deviceaccording to claim 21, wherein the controller is configured to maintainthe amount of unaerosolized liquid adhering to the element within arange of from about 2 to about 20 μl (microliters) duringaerosolization.
 25. An aerosolization device according to claim 21,further comprising a housing having a mouthpiece, the aerosol generatorbeing disposed in the housing for delivery of aerosolized liquid throughthe mouthpiece.
 26. An aerosolization device according to claim 21,wherein the liquid supply system comprises a dispenser for dispensing acertain amount of liquid upon receipt of a dispense signal from thecontroller.
 27. An aerosolization device according to claim 26, furthercomprising a meter for limiting the number of times the dispenserdispenses the amount of liquid during operation of the aerosolgenerator.
 28. An aerosolization device according to claim 21, furthercomprising a heater for heating unaerosolized liquid supplied to theaerosol generator.
 29. An aerosolization device according to claim 28,wherein the heater is adapted to heat the aerosol generator to vaporizethe unaerosolized liquid applied to the aerosol generator.
 30. Anaerosolization device according to claim 28, wherein the heatercomprises an electrical resistance heating element and an electricalpower supply for energizing resistance heating.
 31. A method ofaerosolizing a liquid, the method comprising: providing an aerosolgenerator that is operable to aerosolize a liquid; supplying a liquid tothe aerosol generator from a liquid supply system at a certain flowrate; operating the aerosol generator to aerosolize at least some of thesupplied liquid; sensing an amount of the supplied liquid that remainsunaerosolized; and regulating rate of liquid supply based on the sensedamount of unaerosolized liquid.
 32. A method according to claim 31,wherein the rate of liquid supply is decreased when the sensed amount ofunaerosolized liquid exceeds a certain value.
 33. A method according toclaim 31, wherein the rate of liquid supply is increased when the sensedamount of unaerosolized liquid falls below a certain value.
 34. A methodaccording to claim 31, wherein the aerosol generator comprises a platehaving a plurality of apertures and a vibratable element disposed tovibrate the plate.
 35. A method according to claim 31, wherein the stepof sensing comprises: providing a sensor comprising a piezoelectricelement coupled to the aerosol generator such that variations in theamount of unaerosolized liquid adhered to the aerosol generator causecorresponding variations in electrical characteristics of thepiezoelectric element; and measuring an electrical characteristic of thepiezoelectric element.
 36. A method according to claim 35, wherein theelectrical characteristic measured is selected from a group consistingof impedance, capacitance and inductance.
 37. A method according toclaim 31, wherein the step of sensing comprises: providing an opticalsensor; and detecting with the optical sensor the presence or absence ofunaerosolized liquid in a certain location on the aerosol generator. 38.A method according to claim 37, wherein the certain location is spacedfrom where liquid is supplied to the aerosol generator.
 39. A methodaccording to claim 31, wherein the step of sensing comprises: providinga conductive sensor configured to sense electrical conductivity betweenat least two points on a surface of the aerosol generator on whichunaerosolized liquid adheres, and measuring electrical conductivitybetween the at least two points.
 40. A method according to claim 31,further comprising: maintaining the rate of liquid supply such that theunaerosolized liquid remains within a certain range during operation ofthe aerosol generator.
 41. A method according to claim 40, wherein thecertain range maintained is from about 2 to about 20 μl (microliters).42. A method according to claim 31, further comprising: providing ahousing with a mouthpiece, the aerosol generator being disposed in thehousing for delivery of aerosolized liquid through the mouthpiece;detecting when a user inhales through the mouthpiece; and operating theaerosol generator upon detection of inhalation through the mouthpiece.43. A method according to claim 31, wherein the supply step comprisesdispensing a certain amount of liquid from the liquid supply system forthe aerosol generator.
 44. A method according to claim 43, in which thesupply step further comprises metering the number of times the amount ofliquid is dispensed during operation of the aerosol generator.
 45. Amethod according to claim 31, further comprising: providing a heater forheating unaerosolized liquid supplied to the aerosol generator.
 46. Amethod according to claim 45, further comprising sensing whether any ofthe supplied liquid remains unaerosolized after ceasing the liquidsupply; and operating the heater upon sensing such supplied liquidremaining.
 47. A method according to claim 46, wherein the heatervaporizes the remaining unaerosolized liquid.
 48. A method ofcontrolling supply of a liquid to an aerosol generator, comprising:operating a liquid supply system to supply a liquid to a vibratableaperture element of an aerosol generator; sensing an amount of liquidadhering to the vibratable aperture element; and controlling operationof the liquid supply system to adjust the amount of liquid in contactwith the vibratable aperture element.
 49. A method according to claim48, further comprising vibrating the vibratable aperture element whileoperating the liquid supply system to aerosolize liquid supplied to thevibratable aperture element.
 50. A method according to claim 49, whereinthe step of controlling comprises increasing the liquid supply when thesensed amount of liquid adhering to the vibratable aperture elementfalls below a certain value.
 51. A method according to claim 49, whereinthe step of controlling comprises decreasing the liquid supply when thesensed amount of liquid adhering to the vibratable aperture elementrises above a certain value.
 52. A method according to claim 49, whereinthe step of sensing comprises: providing a sensor comprising apiezoelectric element coupled to the vibratable aperture element suchthat variations in the amount of unaerosolized liquid adhered to thevibratable aperture element cause corresponding variations in electricalcharacteristics of the piezoelectric element; and measuring anelectrical characteristic of the piezoelectric element.
 53. A methodaccording to claim 52, wherein the electrical characteristic measured isselected from a group consisting of impedance, capacitance andinductance.
 54. A method according to claim 49, wherein the step ofsensing comprises: providing an optical sensor; and detecting with theoptical sensor the presence or absence of unaerosolized liquid in acertain location on the vibratable aperture element.
 55. A methodaccording to claim 54, wherein the certain location is spaced from whereliquid is supplied to the vibratable aperture element.
 56. A methodaccording to claim 55, wherein the step of sensing comprises: providinga conductive sensor configured to sense electrical conductivity betweenat least two points on a surface of the vibratable aperture element onwhich unaerosolized liquid adheres, and measuring electricalconductivity between the at least two points.
 57. A method according toclaim 49, further comprising: providing a housing with a mouthpiece, theaerosol generator being disposed in the housing for delivery ofaerosolized liquid through the mouthpiece; detecting when a user inhalesthrough the mouthpiece; and operating the aerosol generator upondetection of inhalation through the mouthpiece.
 58. A method accordingto claim 49, wherein the liquid supply system operation step comprisesdispensing a certain amount of liquid from the liquid supply system forthe aerosol generator.
 59. A method according to claim 58, wherein theliquid supply system operation step further comprises metering thenumber of times the amount of liquid is dispensed during operation ofthe aerosol generator.
 60. A method according to claim 49, furthercomprising: providing a heater for heating unaerosolized liquid suppliedto the aerosol generator.
 61. A method according to claim 60, furthercomprising: sensing whether any of the supplied liquid remainsunaerosolized after ceasing the liquid supply; and operating the heaterupon sensing of the remaining liquid.